It will be recalled that a space telescope comprises optical elements such as mirrors. An example of space telescope, of Korsch type, is shown in FIG. 1a, in which the distances between mirrors are also indicated. A pierced parabolic mirror M1 returns the rays from infinity to the planar mirror M2 which reflects them through the aperture formed in the mirror M1, onto another parabolic mirror M3 via a return mirror Mr. From M3 the rays converge on a focal plane PF. When these elements M1, M2, M3 and Mr are positioned in the telescope in a fixed manner, that is to say with no in-flight servo-positioning mechanism, the telescope is called a passive telescope. When at least one optical element is associated with an in-flight servo-positioning mechanism, the telescope is called an active telescope. Hereinbelow, an active telescope is considered with at least one mirror linked to a servo-control mechanism, for example the mirror M2.
The servo-control mechanism of the mirror has a number of degrees of freedom in rotation and/or translation provided by means of actuators, the mirror being fixed to the servo-control mechanism by a single foot, as shown in FIG. 1b for a mirror M2 (11) linked by a foot 12 to a servo-control mechanism 2 which has 5 degrees of freedom: 3 in translation respectively on the axes x, y and z, and 2 in rotation about the axis y and about the axis x. The servo-control mechanism 2 comprises actuators 21 linked on the one hand to the foot 12 through a plate 23 and on the other hand to the support 22 of the servo-control mechanism which is itself fixed to the frame of the telescope (not represented).
Each mirror, and more particularly the mirror M2 which is installed at the top of the telescope, is subjected to significant accelerations when the satellite onboard which it is installed is launched. This demands a servo-control mechanism capable of withstanding significant acceleration loadings, typically of approximately 1800 N (6 kg weight of the mirror M2 under an acceleration of 30 g, g being Earth's gravity) distributed over all the actuators.
One solution consists in developing linear actuators that withstand strong loads; however, such actuators are not currently available on the market. Such actuators will need to have a significant rigidity which will increase the weight of the mechanism; however, this presents a drawback inasmuch as this excess load is situated in an area of the satellite that does not favour its agility.
Consequently, there currently remains a need for an active space telescope comprising at least one mirror linked to a servo-control mechanism, and that simultaneously gives satisfaction to all of the abovementioned requirements, in terms of weight of the servo-control mechanism and of use of existing actuators.